Twenty years ago, Trevor Griffiths was commissioned by Richard Attenborough to write a movie about the visionary English radical, Thomas Paine. Sadly, the film was never made. But Griffiths has now adapted his magnificent screenplay for the stage. The resulting three-hour play, even if it occasionally reveals its origins, is a moving and informative tribute to the man Michael Foot once called "the greatest exile ever to leave these shores".

Exile is very much Griffiths's theme. The Thetford-born Paine is seen as a restless traveller whose writings on liberty, justice and freedom had an inspirational impact on both the American and French revolutions. Journeying to Philadelphia in 1774, he finds himself enmeshed in the struggle of the 13 colonies to free themselves from British rule, but he becomes disillusioned when victory licenses the rich and powerful. Arriving in Paris in 1790 full of rational optimism about a revolution based on human brotherhood, Paine is horrified when it descends into the bloodbath of the Terror. Yet, although outlawed in England and imprisoned in Paris, Paine dies in the US still believing in the possibility of beneficent revolution.

Griffiths steers us through a welter of great events: everything from Washington's military triumph to Danton's political downfall. Through it all he presents us with a wonderfully clear, unsentimental portrait of Paine himself: a mulish innocent with little sense of realpolitik, a writer driven by passion rather than profit, and a born educator who takes an enslaved African boy under his wing on his arrival in Philadelphia.

Griffiths has the priceless ability to show the power of Paine's ideas and to make history come alive. Commissioned by Washington to come up with a rushed pamphlet on the American Crisis, Paine asks "Will it do, General?" to which Washington replies "It will do, sir." Behind the simple language lies a tide of emotion and belief.

The corresponding virtue of Dominic Dromgoole's fine production is that it never loses sight of the individuals beneath the epic events. John Light shines out strong and clear as a doggedly uncompromising Paine who never loses his faith in reason and the potential for revolution. And there is first-rate support from Keith Bartlett as the jovial narrator Benjamin Franklin, Jamie Parker as a laconic Jefferson and Alix Riemer as Paine's French translator, helpmate and lover, who stuck with him to the last. Adorned with rousing songs by Stephen Warbeck, this is an intelligent historical spectacle packed with contemporary resonance.